The present invention relates to a method and apparatus for pre-treating a metal sample (referred to as an xe2x80x9canalytical metal samplexe2x80x9d hereinafter) subjected to metal analysis. Particularly, the present invention relates to a pre-treatment method and pre-treatment apparatus for removing contaminants adhering to and/or adsorbed on the surface of a metal sample before analysis of trace elements in a metal. Also, the present invention relates to an apparatus comprising the pre-treatment apparatus, for analyzing elements in a metal.
The trace elements of steel, for example, oxygen, carbon, nitrogen, and sulfur influence the material properties of steel, such as ductility, processability, etc., and accurate quantitative analysis is required. This is generally widely indicated in the fields of iron and steel industry and metal material industry with increases in purity of metal materials. Therefore, an apparatus and method for analyzing the elements in a metal with high accuracy and high operationality is required.
In order to comply with this requirement, the contaminants produced on the surface of an analytical metal sample must be removed in the step of preparing the sample. For example, when organic materials are adsorbed on the surface of the sample, or surface oxidation occurs by an atmosphere of carbon dioxide gas, air or the like, oxygen analysis of steel causes significant error in the analytical value. Therefore, in a melting-infrared absorption method in an inert gas, which is widely used as an analysis method for trace oxygen in a metal, the surface of the analytical metal sample is cleaned by an electropolishing method or chemical polishing method before analysis. This method can remove most of the surface contaminants. However, actually, the surface of the analytical metal sample is again contaminated with the chemicals used for cleaning and polishing, and the contaminants removed, or again oxidized by the air before measurement by an analysis apparatus. For example, in quantitative analysis of oxygen, the influence of such residual contamination and re-contamination on the analytical value corresponds to 1 to 2 ppm in terms of concentration, and causes error in a ppm level (Iron and Steel, Vol. 85, p. 138(1999), etc.). Particularly, on the clean surface of a metal, adsorption of atmospheric materials, oxidization, or the like momentarily occurs, and it is thus important for improving analysis accuracy to remove a re-contaminated portion or a portion contaminated with residual materials.
Under the above background, Japanese Unexamined Patent Application Publication No. 8-211043 discloses a method in which an electric discharge is induced in an analytical metal sample in a low-pressure gas to remove contaminants from the surface, and then transferred to an analysis apparatus for analyzing carbon. This electric discharge cleaning is referred to as xe2x80x9csputtering treatmentxe2x80x9d.
However, in the method disclosed in Japanese Unexamined Patent Application Publication No. 8-211043, one counter electrode is used for the electric discharge of the metal sample, and a sample support on which the metal sample is mounted has a plate form. Therefore, in order to clean the back side of the sample (the surface in contact with the sample support) by sputtering, the analytical metal sample must be rotated or reversed. However, the operation of reversing the sample is complicated, and the operation is likely to again bring the analytical metal sample into contact with the air or drop the sample from the sample support. When the sample drops from the sample support, analysis can no longer be performed. Therefore, in the method disclosed in Japanese Unexamined Patent Application Publication No. 8-211043, in fact, the back side (in contact with the sample support) of the metal sample, which occupies a large area, cannot be cleaned by sputtering.
Japanese Unexamined Patent Application Publication No. 11-316220 discloses a method in which an analytical metal sample is sputtered in an inert atmosphere in a pre-treatment chamber connected to an analysis apparatus, and then the sample from which contaminants are removed from the surface is moved to an elementary analysis apparatus without being exposed to the air. In this method, the side of the metal sample is point-supported, and thus contaminants can be simultaneously removed from almost the whole area of the surfaces of the analysis sample.
However, the analytical metal sample is point-supported to cause difficulties in setting the analytical sample, and a great problem of operationality remains.
An object of the present invention is to provide a pre-treatment apparatus and pre-treatment method which can resolve the problems of the conventional techniques, and can effectively remove contaminants from the surface of a metal sample in order to improve the accuracy of quantitative analysis of trace components of a metal. Another object of the present invention is to provide an analysis apparatus comprising the pre-treatment apparatus.
The present invention provides an apparatus for pre-treating an analytical metal sample, comprising (1) a treatment chamber having a sample charging port which can be opened and closed and provided at the top of the chamber, a sample discharging port which can be opened and closed and provided at the bottom of the chamber, and a gas inlet and gas outlet, (2) a sample carrying bar connected to a sample holder also used as a sputtering electrode, and provided to pass through at least one side wall of the treatment chamber so as to be substantially horizontally movable and axially rotatable, and (3) a sputtering counter electrode at least having portions arranged opposite to each other in a region not inhibiting the charge and discharge of the analytical metal sample so that the sample holder can be arranged in the counter electrode.
In the pre-treatment apparatus, the contact area between the sample and the sample holder is preferably 10% or less of the surface area of the analytical metal sample.
In the pre-treatment apparatus, the counter electrode at least having portions arranged opposite to each other preferably has a cylindrical shape.
The present invention also provides an elementary analysis apparatus for a metal, comprising a sample inlet port connected to a portion below the sample discharging port of the pre-treatment apparatus.
The present invention further provides a pre-treatment method for elementary analysis of a metal using the pre-treatment apparatus, comprising the steps of (1) charging an analytical metal sample in the sample holder through the sample charging port, (2) evacuating the treatment chamber to form a reduced pressure atmosphere, and then controlling the inside of the treatment chamber to a predetermined pressure of 100 Pa to 1000 Ps by using an inert gas, (3) moving the analytical metal sample on the sample holder by the sample carrying bar to a position in the sputtering counter electrode at least having portions opposite to each other, (4) applying a voltage between the sample-side electrode and the sputtering counter electrode to clean the surface of the analytical metal sample by sputtering, (5) moving the sample holder to a position above the sample discharging port by the sample carrying bar, (6) rotating the sample carrying bar to move the analytical metal sample to an elementary analysis apparatus through the sample discharging port.